Device for assisting the piloting of a rotorcraft

ABSTRACT

A device for assisting the piloting of a rotorcraft, the rotorcraft having a flight control ( 10 ) for controlling a rotor ( 20, 21 ) via at least one linkage ( 35 . An additional force is generated by at least one piloting assistance means ( 100 ) mechanically linked to the linkage ( 35 . The additional force is a function of the position of the flight control ( 10 ) and of an instantaneous force as measured on the linkage ( 35 ).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. Ser. No. 12/814,687, filed Jun.14, 2010, which claims priority to French Patent Application No. FR0902913 dated Jun. 16, 2009, the disclosures of which are incorporatedin its entirety by reference herein.

FIELD OF THE INVENTION

The present invention relates to a device for assisting the piloting ofa rotorcraft, and in particular a helicopter.

BACKGROUND OF THE INVENTION

Conventionally, a rotorcraft commonly includes a main lift rotorprovided with a plurality of blades.

The blades of the main lift rotor describe a very flat cone having aplane of rotation that is perpendicular to the general lift generated bysaid main rotor. This general lift of the main rotor may then beresolved into a vertical lift force proper and a horizontal force thatserves to cause the helicopter to move in translation. Consequently, themain rotor does indeed provide the rotorcraft with lift.

In addition, on a helicopter, by controlling the shape and the tilt ofsaid cone relative to the frame of reference of the helicopter, a pilotcan control the advance of the helicopter and direct it accurately.

In order to act on the cone, the blades are caused to flap so as tomodify their angle of inclination relative to the drive plane of themain rotor, said drive plane being perpendicular to the mast of the mainrotor. By varying the pitch of a blade, the lift it generates is varied,thereby causing the flapping of said blade to vary.

Consequently, the helicopter is provided with specific means for causingthe pitch of each blade to vary, and consequently for varying theaerodynamic angle of attack of each blade relative to the incidentstream of air through which the blade passes.

In order to control the general lift of the main rotor, both inmagnitude and in direction, the helicopter pilot thus acts generally onthe value of the pitch angle of each blade by causing the blade to turnabout its longitudinal pitch axis. Thus, when the pilot orders acollective variation of pitch, i.e. an identical variation in pitch forall of the blades, the pilot causes the magnitude of the lift generatedby the main rotor to vary, thereby controlling the altitude and thespeed of the helicopter.

In contrast, collective pitch variation has no effect on the directionof this general lift.

In order to modify the direction of the general lift generated by themain rotor, it is necessary to incline said cone by varying pitch in amanner that is not collective, but rather that is cyclic. Under suchcircumstances, the pitch of a blade varies as a function of its azimuthangle and during one complete revolution it passes between a maximumvalue to a minimum value that are obtained at opposite azimuth angles.

Cyclic variation of the pitch of the blades gives rise to cyclicvariation in the lift from the blades and thus to variation in the angleof inclination of the cone. By cyclically varying the pitch of theblades, the pilot controls the attitude of the aircraft and its movementin translation.

The pilot's pitch flight controls, a collective pitch lever and a cyclicstick, are generally connected to the blades via mechanical connectionsknown as “linkages”, which linkages are secured to the non-rotatingplate of a cyclic swashplate. The rotating plate of the cyclicswashplate is mechanically connected to each blade via a respectivepitch control rod.

More precisely, primary roll and pitch linkages connect the cyclic stickto a mixer, the mixer being connected to the non-rotary plate of thecyclic swashplate by secondary linkages. In addition, the collectivepitch lever is connected to the mixer via a collective primary linkage.Under such circumstances, a flight control is connected to a rotor via aroll and pitch linkage or collective linkage, both of which are providedin succession with a primary linkage and a secondary linkage.

A movement of the cyclic stick causes the primary roll or pitch linkageto move and consequently causes the corresponding secondary linkage(s)to move via the mixer.

In contrast, a movement of the collective pitch lever gives rise to amovement of the collective primary linkage and then of the secondarylinkage via the mixer.

Nevertheless, since the forces that need to be exerted are large, aservo-control is generally made available in each secondary linkage. Forexample, in a light helicopter, there is provided in principle oneservo-control for pitch control, referred to as the “pitchservo-control” for convenience, and two servo-controls for roll to leftand to right for piloting in roll.

When the pilot seeks to modify the collective pitch of the blades,action on the collective lever causes all three servo-controls to raiseor to lower the cyclic swashplate as a whole, i.e. both the non-rotaryplate and the rotary plate of the cyclic swashplate.

The pitch control rods are then all moved through the same distance,which implies that the pitch of all of the blades varies through thesame angle.

In contrast, in order to apply cyclic pitch variation to the blades soas to direct the helicopter in a given direction, the pilot causes atleast one servo-control to move by tilting the cyclic stickappropriately in the desired direction.

The cyclic swashplate then does not move vertically, but instead tiltsrelative to the mast of the main rotor. Each pitch control rod is thusmoved as a function of the intended target so as to generate appropriatecyclic variation of the pitch of each blade.

Furthermore, the linkages are provided with at least one link rod and atleast one crank means for connecting the pilot's flight controls to theservo-controls. In addition, provision may also be made for a phasingunit that enables the cyclic swashplate to tilt about two mutuallyperpendicular axes for use in heavy helicopters.

Similarly, the flight controls of a helicopter include a yaw controlconnected to a tail rotor by a yaw linkage that passes via the mixer.

The linkages are thus generally very long and heavy, particularly theyaw control linkage.

The members of the linkages give rise to friction forces that may beconsiderable for linkages of great length. Under such conditions thepilot may have difficulty in moving the cyclic stick or the collectivepitch lever, given the amount of force required.

A first solution consists in using electric flight controls as suggestedin document WO 2005/002963 or US 2007/0102588 (now U.S. Pat. No.7,229,046). Nevertheless, that first solution is difficult to implement,in particular on existing rotorcraft.

Consequently, helicopter manufacturers have remedied the problem asposed by adding assistance systems that may be hydraulic or pneumatic.Known assistance systems consist in a block of actuators acting merelyas a force-multiplying relay unit, with the block of actuators beingarranged for example between bottom crank means and the mixer, forexample.

Nevertheless, such assistance systems are bulky and heavy. Furthermore,they run the risk of hydraulic or pneumatic leakage, leading to a lossof effectiveness.

Finally, the gas in pneumatic assistance systems is sensitive tovariations in temperature, unfortunately all too frequent in aviation,in particular because of operating at different altitudes, and thefluids used in hydraulic assistance systems possess polluting chemicalcompounds.

In addition, rotorcraft conventionally include an autopilot system forstabilizing the rotorcraft and/or for reducing the pilot's workload.

Fitting an autopilot system may possibly lead to “series” actuatorsbeing put into place in series in each linkage between a flight controland the controlled rotor.

The series actuators are intended for stabilizing the rotorcraft. Thus,the series actuators are generally very fast, but with little authorityin amplitude.

Document EP 1 037 130 presents a “series” actuator suitable for beingcontrolled by a computer to stabilize the machine.

A sensor sends information about an order given by a control stick tothe computer. The computer then makes use of piloting relationships tocontrol the series actuator in order to stabilize the helicopter.

Furthermore, an actuator known as a “parallel” actuator, or indeed as a“trim” actuator, is placed in parallel with each linkage.

Unlike series actuators, parallel actuators are controlled by autopilotmeans to control the movements of the helicopter. Thus, parallelactuators are generally slow, but have considerable authority inamplitude.

The autopilot controls the parallel actuators to maneuver therotorcraft.

Furthermore, parallel actuators are used as anchors for seriesactuators. The autopilot continuously activates the series actuators inorder to stabilize the rotorcraft. Without some additional action, themovements of the series actuators would be fed back to the pilot'sflight controls.

By anchoring the associated flight controls, the parallel actuatorsprevent the movements of the series actuator from being fed back to theflight controls, e.g. the cyclic stick.

The parallel actuators also serve to anchor the flight controls.

In a first variant, a parallel actuator includes a motor suitable formoving an outlet shaft that is connected in parallel to a linkage.Between the motor and the outlet shaft, the parallel actuator isprovided in particular with gearing, a spring box generating adetermined force relationship, and a safety pin.

In another variant described in patent FR 2 708 112, the parallelactuator includes in particular in succession: a motor, a reversiblegearing, a position sensor, a safety device, and an outlet shaft.

Control means activated by an autopilot then control the motor togenerate a force relationship.

According to document US 2005/0173595 (now U.S. Pat. No. 7,108,232), theparallel actuator is an actuator suitable for generating a forcerelationship by being controlled by dedicated means.

Furthermore, dampers are provided in the linkages in order to stiffenthe flight controls as a function of the speed at which the flightcontrols are moved.

Consequently, the state of the art includes rotorcraft having a pilotingassistance device, provided in particular with a hydraulic block or witha plurality of series and parallel actuators.

Such a device is necessarily bulky, heavy, and expensive.

SUMMARY OF THE INVENTION

An object of the present invention is thus to propose a multipurposepiloting assistance device that enables the above-mentioned limitationsto be overcome.

According to one embodiment of the invention, the device is used as apart of a method of assisting the piloting of a rotorcraft. Therotorcraft includes a flight control for controlling a rotor via atleast one linkage, and is remarkable in that an additional force isgenerated using piloting assistance means mechanically linked to said atleast one linkage, being arranged in parallel with said linkage, theadditional force being a function of a setpoint force relating to theposition of the flight control and a function of an instantaneous forceas measured on the linkage.

Advantageously, the method is applied to each control linkage by placingpiloting assistance means in parallel on each control linkage.

It should be observed that autopilot means may control the pilotingassistance means to cause them to perform the functions of existingdampers and parallel actuators.

Thus, the invention makes it possible to use piloting assistance meansto replace parallel actuators, dampers, and the hydraulic blockimplemented in the state of the art. It can be understood that thissimplifies the architecture of flight controls and reduces their weight.

In addition, depending on the position of the control stick and on themeasured instantaneous force, the piloting assistance means act on thelinkage to facilitate the pilot's work, regardless of the amount offriction exerted on the linkage.

Unlike existing parallel actuators that are rather of a passive typeusing a torsion spring, thereby generating a force that is constant overtime, the invention provides an active method that takes account of theforce actually exerted on the linkage. Thus, even if the frictionexerted on the linkage increases with increasing wear of the linkage,the pilot does not need to provide additional effort to counter it,since compensation is provided by the piloting assistance means.

One method of using the inventive device may also include performing oneor more of the following steps:

measuring in real time an instantaneous force exerted on the linkage;

measuring the position of the flight control, e.g. a cyclic stick;

using at least one pre-established force relationship to determine asetpoint force that ought to be felt by the pilot operating the flightcontrol when the flight control is at the measured position, and thendetermining the additional force to be equal to the difference betweenthe setpoint force and the instantaneous force; and

determining the setpoint electric current to deliver to the pilotingassistance means in order to cause the piloting assistance means togenerate the additional force, and then electrically powering thepiloting assistance means in compliance with the setpoint current.

In addition, the pre-established force relationship is optionallychanged as a function of flying conditions.

In a first variant, the pre-established force relationship is changedmanually by the pilot, e.g. to go from a spring type force relationshipto a friction type force relationship. Such a spring type forcerelationship possesses prestress associated with a force gradient havingone or two slopes, whereas a friction type force relationship makes useof a constant force.

In a second variant, the pre-established force relationship is changedautomatically by autopilot means.

Thus, it is possible to provide a force relationship that presents, in agraph plotting flight control position along the abscissa and force tobe delivered up the ordinate:

the appearance of a straight line of shallow slope while the rotorcrafthas a forward speed that is low, i.e. less than 50 knots for example(where 1 knot corresponds to 1.852 kilometers per hour); and

the appearance of a straight line having a steep slope once the forwardspeed of the rotorcraft is large, i.e. greater than a threshold of 50knots, for example.

In a third variant, for the piloting assistance means comprising atleast one electric motor suitable for acting on the linkage to generatethe additional force, the method comprises the steps of:

measuring the speed of rotation of the electric motor by differentiatingthe angular position of the electric motor; and

changing the force relationship as a function of the speed of rotation.

By making these changes to the force relationship, it is possible toavoid implementing a damper in the linkage.

Furthermore, in a rotorcraft, there are numerous limits that the pilotneeds to take account into at all times while flying.

Most presently-constructed helicopters are fitted with one or twoturbine engines, with power being taken from a turbine, possiblymechanically independently from the compressor assembly of a freeturbine engine. The free turbine of an engine rotates at 20,000 to50,000 revolutions per minute, so a speed-reducing gearbox is needed forthe connection to a rotor, since the rotor has a speed of rotation lyingsubstantially in the range 200 to 400 revolutions per minute for a mainlift rotor: this is known as the main gearbox (MGB).

The limits laid down by the manufacturer and that need to be taken intoaccount by the pilot then include limits concerning the main gearboxand/or limits concerning the engine, e.g. a maximum duration for whichthe engine may be used at a particular speed.

Under such circumstances, in a fourth variant the force relationship ischanged on reaching one of said limits, changing from a forcerelationship having a shallow slope to a force relationship having asteep slope. The pilot's flight control then appears stiffer. Thus, thepilot is informed that a limit has been reached in the power plant or inthe main gearbox.

Furthermore, for piloting assistance means including a plurality ofconnection plugs suitable for receiving a plurality of differentconnectors of the rotorcraft, the method consists in the pilotingassistance means determining said at least one force relationship as afunction of which plugs are connected to a connector.

The same piloting assistance means may then be implemented on anylinkage, thereby enabling said piloting assistance means to bestandardized and thus reducing the fabrication and purchase costs ofsuch piloting assistance means.

For example, the piloting assistance means may be connected to theelectrical circuit of the rotorcraft via a plug provided with first,second, third, and fourth orifices.

Thus:

if the connector co-operates with the first orifice of said plug, thepiloting assistance means deduce that they are connected to the rolllinkage and make use of the pre-established force relationshipsappropriate for the roll linkage;

if the connector co-operates with the second orifice of said plug, thepiloting assistance means deduce that they are connected to the pitchlinkage and make use of the pre-established force relationshipsappropriate for the pitch linkage;

if the connector co-operates with the third orifice of said plug, thepiloting assistance means deduce that they are connected to thecollective linkage and make use of the pre-established forcerelationships appropriate for the collective linkage; and

if the connector co-operates with the fourth orifice of said plug, thepiloting assistance means deduce that they are connected to the yawlinkage and make use of the pre-established force relationshipsappropriate for the yaw linkage.

Advantageously, for the additional force being generated with the helpof at least one brushless electric motor of the piloting assistancemeans, the method consists in disconnecting the electric motor as soonas its electricity consumption exceeds a predetermined operatingthreshold. Disconnection may be electrical or mechanical disconnection.

Excessive electricity consumption tends to indicate that the pilotingassistance means are faulty. The electric motor is thereforedisconnected from the linkage in order to avoid blocking it.

Furthermore, it is optionally possible to determine the setpointelectric current for supplying to the piloting assistance means by usingbroadband vector control.

The electric motor is then controlled as a function of a result that itis to achieve. Vector control via mathematical transformations enablesthe direction and the magnitude of the magnetic field to be controlleddynamically and thus enables the torque and the direction of rotation ofthe rotary member of the electric motor to be controlled, i.e. the driverotor of the electric motor.

Use of broadband vector control enables torque to be controlled, whileavoiding modulating the magnetic field so as to avoid the pilot feelingtorque undulations.

Reference can be made to the literature to obtain more information onthis topic.

Furthermore, for the rotorcraft including autopilot means suitable forcontrolling at least one series actuator in the linkage, the methodincludes the step of using the piloting assistance means to anchor theflight control dynamically when the autopilot means operate the seriesactuator.

Thus, an order given to the series actuator having the effect ofstabilizing the rotorcraft does not influence the flight control. Thepilot does not feel through the flight control thelengthening/shortening of the series actuator under the control of theautopilot means.

For example, by instructing the electric motor of the pilotingassistance means to remain in a given position, the autopilot meansanchor the flight control.

The invention thus enables flight controls to be anchored dynamically.

It should be observed that the force relationship of the pilotingassistance means give rise in fact to the flight control being anchoredmechanically in a manner that is static. Thus, mere contact with aflight control, e.g. as a result of the pilot's knee coming into contactwith a stick, does not generate sufficient force to induce any movementin the associated linkage.

Nevertheless, it should be understood that it remains possible to anchorthe flight controls mechanically by giving rise to relatively highlevels of friction in appropriate sectors of the linkage.

In addition, for a rotorcraft including autopilot means, the pilotingassistance means do not generate any additional force when under thecontrol of the autopilot.

Since the pilot is not operating the pilot's control means, the pilotingassistance means have no need to generate an additional force.

However, if the pilot operates the control means so as to modify theinstantaneous force by a predetermined value, the method consists indisengaging the autopilot means so that the autopilot means no longercontrol the piloting assistance means.

When the pilot acts on the pilot's flight control, the instantaneousforce increases or diminishes. The variation in this instantaneous forceis thus detected immediately. Since the pilot has priority over theautopilot means, the autopilot means are then disengaged.

Furthermore, if the autopilot means is linked with at least one linkagefor stabilizing the rotorcraft, then in an emergency mode, saidautopilot means control the piloting assistance means to perform astabilizing function via a specific engagement signal relating to astabilization order.

Clearly, the associated flight control is no longer anchored by thepiloting assistance means.

Furthermore, in order to verify proper operation of the linkage havingthe piloting assistance means arranged thereon, the method includes thesteps of:

determining a force generated by said piloting assistance means using apre-established electricity consumption relationship giving saidgenerated force as a function of the electricity consumption of saidpiloting assistance means;

determining a real friction force equal to the difference between aninstantaneous force exerted on said linkage as measured in real time andsaid generated force;

determining an ideal friction force for said linkage using apre-established friction relationship; and

signaling an anomaly when said real friction force exceeds said idealfriction force by a given threshold, e.g. once the real friction forceis equal to twice said ideal friction force.

Furthermore, for said piloting assistance means including an electricmotor controlled by control means, said control means are advantageouslyprovided with a main computer unit and with a monitoring computer unit,each determining said additional force. The piloting assistance meansare then deactivated if the additional force as determined by the maincomputer unit differs from the additional force as determined by saidmonitoring computer unit.

More precisely, the main computer unit controls the electric motor togenerate the additional force, while the monitoring computer unitperforms verification and deactivates the piloting assistance means,where appropriate.

The invention also provides piloting assistance means suitable forimplementing the method of the invention, the piloting assistance meansbeing provided with at least one electric motor controlled by controlmeans, the electric motor being connected to an outlet shaft via gearingand fuse means in succession.

The fuse means then comprise:

a first wheel provided both with teeth on an outer periphery thatco-operate with said gearing, and with driving teeth, said driving teethbeing suitable for moving axially relative to said gearing;

driven teeth arranged on said outlet shaft, suitable for co-operatingwith said driving teeth; and

a stationary electrical coil for attracting said driving teeth againstsaid driven teeth when it is electrically powered by control means.

It should be observed that two configurations are possible:

either the driving teeth are secured to said first wheel, with saidfirst wheel being suitable for moving axially relative to the gearing,e.g. via fluting;

or else the driving teeth are suitable for moving axially relative tothe first wheel, e.g. via fluting.

Thus, the piloting assistance means enable the above-described method tobe implemented and advantageously replace a hydraulic block, a parallelactuator, and a damper.

In addition, the piloting assistance means may include at least onefirst position sensor suitable for determining the angular position ofthe electric motor, and/or at least one second position sensor forsensing the position of the outlet shaft.

The first and second sensors both serve to determine the position of theflight control controlling the linkage fitted with the pilotingassistance means.

In the event of the first sensor failing, the second sensor remainsusable, and vice versa.

In addition, if the first and second sensors provide contradictoryinformation, the control means are in a position to generate a warning.Each type of sensor has its own role, but comparing the information theytransmit provides means for monitoring said equipment.

In addition, the first and second sensors are advantageously providedredundantly, the piloting assistance device then having two firstsensors and two second sensors. The control means can then easilyisolate a faulty sensor, i.e. a sensor giving information that does notcorrespond to the information provided by the other three sensors.

Finally, the invention also provides a device for assisting the pilotingof a rotorcraft and suitable for implementing the method as describedabove, said rotorcraft being provided with a flight control forcontrolling a rotor via at least one linkage provided with a pluralityof rods including at least one intermediate rod and link means. Thedevice then comprises:

an instantaneous force sensor arranged in the intermediate rod;

determination means for determining the position of the flight control;

piloting assistance means of the invention having at least one electricmotor controlled by control means to drive an outlet shaft connecteddirectly or indirectly to the link means in parallel with the linkage,the piloting assistance means including at least a first position sensorsuitable for determining the angular position of the electric motor,and/or at least a second position sensor for sensing the position of theoutlet shaft.

The device of the invention thus limits the elements needed forassisting the pilot, thereby optimizing the weight of the device.

The piloting assistance means of the invention are fast, while havinggreat authority. Consequently, they are perfectly capable of performingthe function of a conventional series actuator.

Nevertheless, the piloting assistance device may optionally include atleast one series actuator arranged between the rotor and the link means.

Furthermore, the piloting assistance device is optionally provided atleast with autopilot means suitable for controlling the pilotingassistance means and optionally the series actuator.

In addition, in order to anchor the flight control mechanically, thedevice is optionally provided with a friction unit arranged between theflight control and the series actuator in order to generate a frictionforce greater than the friction force of the linkage between the seriesactuator and the rotor, where appropriate between the series actuatorand a servo-control.

Finally, for the rotorcraft being provided with at least two linkages,each provided with a plurality of rods including at least intermediaterod and link means, the piloting assistance device then includes:

an instantaneous force sensor arranged in said intermediate rod of eachlinkage; and

a single piloting assistance means of the invention per linkageconnected to the link means in parallel with the associated linkage.

Furthermore, for the electric motor being connected to an outlet shaftsuccessively via gearing and fuse means, the fuse means comprise:

a first wheel provided both with teeth on an outer periphery thatco-operate with the gearing, and with driving teeth on an innerperiphery, the driving teeth being suitable for moving axially relativeto the gearing;

driven teeth arranged on the outlet shaft, suitable for co-operatingwith the driving teeth; and

a stationary electrical coil for attracting the driving teeth againstthe driven teeth when it is electrically powered by a control means.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and its advantages appear in greater detail from thefollowing description of embodiments given by way of illustration withreference to the accompanying figures, in which:

FIG. 1 is a view of a rotorcraft provided with a prior art pilotingassistance device;

FIG. 2 is a diagram showing a piloting assistance device of theinvention having rotary piloting assistance means;

FIG. 3 is a diagram showing a piloting assistance device of theinvention having linear piloting assistance means;

FIG. 4 is a diagram explaining the method of the invention;

FIG. 5 is a diagram explaining the piloting assistance means;

FIG. 6 is an exploded view of the fuse means of the piloting assistancemeans; and

FIG. 7 is an isometric view of the piloting assistance means.

Elements that are present in more than one of the figures are given thesame references in each of them.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a view of a rotorcraft G having a prior art pilotingassistance device.

The rotorcraft G has flight controls 10 connected to the main lift andadvance rotor 20 and to the tail rotor 21 by linkages 35. In particular,the flight controls 10 comprise two sets of rudder pedals 11 for actingon the pitch of the blades of the tail rotor 21, together with twocyclic sticks 12 and two collective pitch levers 13 for modifying thepitch of the blades of the main lift rotor 20 and the pitch of theblades of the tail rotor 21.

In order to control the rotorcraft G in yaw, the rudder pedals 11 areconnected together by a yaw jackshaft 11′ controlling a servo-control 22for modifying the pitch of the blades of the tail rotor 21 via a yawlinkage 31 that comprises in succession:

a bottom first rod 41;

crank means 42;

a second rod 43;

a hydraulic block 44;

a third rod 45;

collective pitch and yaw coupling means 46;

a fourth rod 47;

a mixer 48;

a fifth rod 49; and

a control system 50 having a control cable and pulleys, and a seriesstabilizer actuator 101 controlled by a computer of autopilot means.

Similarly, the collective pitch levers 13 are connected together by acollective pitch jackshaft 13′, the collective pitch jackshaft 13′controlling the servo-controls 23 associated with the cyclic swashplatesof the blades of the main rotor 20 via a collective linkage 34. Thiscollective linkage 34 comprises in particular and in succession: a firstrod 51, crank means 52, a second rod 53, a hydraulic block 44, a thirdrod 55, collective pitch and yaw coupling means 46, a fourth rod 57, amixer 58, and first, second, and third top rods 1, 2, and 3.

In addition, the cyclic sticks 12 are connected together by a pitchjackshaft 12′ and a roll jackshaft 12″.

To control the rotorcraft G in roll, the bottom end of a cyclic stick 12is connected to servo-controls 23 associated with the cyclic swashplatesof the blades of the main rotor 20 via a roll linkage 32. The rolllinkage 32 comprises in succession: a first rod 61, crank means 62, asecond rod 63, a hydraulic block 44, a third rod 64 having a seriesstabilizer actuator 65 controlled by a computer of autopilot means, aphasing unit 66, three fifth rods 67, a mixer 48, and first, second, andthird top rods 1, 2, and 3.

Finally, to control the rotorcraft G in pitch, the pitch jackshaft 12′is connected to servo-controls 23 associated with the cyclic swashplatesfor the main rotor blades 20 via a pitch linkage 33. This pitch linkage33 comprises in succession: a first rod 71, crank means 72, a second rod73, a hydraulic block 44, a third rod 75, a fourth rod 76 having aseries stabilizer actuator 77 controlled by a computer of autopilotmeans, a phasing unit 66, three fifth rods 67, a mixer 48, and first,second, and third top rods 1, 2, and 3.

It should be observed that depending on requirements and safety, aplurality of series actuators may be arranged in a given linkage.

Finally, each linkage has a parallel actuator 4 and a damper 5.

FIG. 2 is a diagram showing a piloting assistance device of theinvention fitted with piloting assistance means 100.

In order to modify the pitch of a blade of a rotorcraft rotor, the pilotuses a flight control 10 connected to a servo-control 23 by a linkage35. The servo-control 23 then modifies the angle of inclination of acyclic swashplate 20′ so as to end up modifying the pitch of thecorresponding blade 20 as required.

According to the invention, a single piloting assistance means 100 isarranged on each linkage, possibly associated with a series actuator 86.Consequently, and unlike the known state of the art, no use is made of aparallel actuator, nor of at least one series actuator and damper perlinkage assisted by a hydraulic block, with use being made at most of asingle piloting assistance means 100 and at least one series actuator86.

For example, the cyclic stick 12 of the flight controls 10 is connectedby a linkage 35, e.g. a pitch linkage, to a servo-control 23 suitablefor controlling the cyclic swashplate 20′.

In order to connect the flight controls 10 to a servo-control 23, thelinkage 35 then includes an intermediate rod 81, link means 82 suitablefor performing rotary movement about a first fastener axis AX1, asecondary second rod 84 provided with friction means 85 and at least oneseries actuator 86, a phasing unit 66, a fourth rod 67, a mixer 48, anda top rod 2. It should be observed that the link means are provided witha first branch 83 hinged to the intermediate rod 81 and secured to afirst free end of a second branch 82 of the link means, the secondbranch 82 being hinged to the secondary second rod 84.

Optionally, the link means may include a triangular member, with twosides of the triangular member being secured to the first and secondbranches to form triangular link means.

In addition, the piloting assistance device includes piloting assistancemeans 100 arranged in parallel with the linkage 35, being hinged to asecond free end of the second branch 82 of the link means, eitherdirectly or via a link rod 87.

Under such circumstances, the piloting assistance device is providedwith an instantaneous force sensor 88 secured to the intermediate rod81. For example, an instrumented rod is used that has at least oneconventional strain gauge type force sensor, possibly implementing aWeston bridge.

In a variant, it is possible to envisage providing a movement sensorthat measures a deformation.

In addition, a single sensor may not be sufficiently reliable, dependingon the safety constraints that need to be satisfied, so the instrumentedrod may have three instantaneous force sensors 88. Using two sensorswould not be any more satisfactory, a priori, insofar as it would bedifficult to determine which sensor is faulty in the event of thesensors not agreeing.

The instantaneous force sensor then delivers first information in realtime over a first wire connection 91 relating to the instantaneous forceexerted on the linkage 35 to control means 104 of the pilotingassistance means.

Additionally, the piloting assistance device possesses determinationmeans 89 for determining the position of the flight control.

In FIG. 2, the determination means 89 comprise an angle sensor, e.g.arranged at the bottom end of the control means. The angle sensor sendssecond information in real time over a second wire connection 92 to thecontrol means 104 of the piloting assistance means.

Below, it is explained that in a variant the means 89 for determiningthe position of the flight control 10 may be incorporated in thepiloting assistance means 100.

Finally, FIG. 2 shows autopilot means suitable for controlling thecontrol means 104 of the piloting assistance means 100 and the seriesactuator 86, respectively via third and fourth wire connections 93 and94.

Thus, depending on requirements, the control means 104 instruct theelectric motor 105 to turn. This motor acts via gearing 102 and fusemeans 103 to turn an outlet shaft 101. The outlet shaft 101 turns asrepresented by double-headed arrow F1 giving rise to movement intranslation of the link rod 87 along its longitudinal axis followed bytilting of the second branch 82 of the link means about its first pivotaxis AX1.

With reference to FIG. 3, in another embodiment, the piloting assistancemeans comprise linear piloting assistance means.

The electric motor 105 in the piloting assistance means does not giverise to rotation but rather to movement in translation of the outletshaft 101 along its extension/retraction axis, as represented bydouble-headed arrow F2.

There is then no need to have a link rod between the outlet shaft andthe second branch 82.

Independently of the variant implemented, depending on the instantaneousforce as measured by the instantaneous force sensor 88 and depending onthe position of the flight control as determined by the determinationmeans 89, the control means 104 of the piloting assistance means 100generate an additional force on the linkage 35 by moving the secondbranch 82.

Depending on requirements, the piloting assistance means block theflight control by generating a complementary force that opposes orassists the pilot in moving the linkage.

For example, if the flight control and the piloting assistance meansboth tend to generate turning of the link means about the first fasteneraxis in the same direction, then the additional force tends to assistthe pilot.

In contrast, if the flight control and the piloting assistance meanstend to generate pivoting of the second branch of the link means aboutthe first fastener axis in opposite directions, then the additionalforce is an opposing additional force that tends to block the flightcontrol.

Furthermore, when the autopilot means 90 cause the series actuator tolengthen or shorten, the piloting assistance means compensate themovement generated by the series actuator via its servo-control logic inorder to anchor the flight control.

In addition, when the autopilot 90 is activated, the autopilot means 90control the piloting assistance means 100, taking the place of thepilot. Consequently, there is no need to generate an additional force inorder to assist the pilot.

In contrast, as soon as the pilot takes back control of the flightcontrol 10, the autopilot means are automatically deactivated.

More precisely, by moving the flight control 10, the pilot willsignificantly increase or decrease the instantaneous force measured bythe instantaneous force sensor 88. As soon as the control means 104receive an instantaneous force variation that is greater than or equalto a predetermined threshold, the control means 104 requestdisengagement of the autopilot means 90.

Furthermore, when the autopilot means 90 cause the series actuator tolengthen or shorten, the piloting assistance means 100 automaticallyanchor the flight control 10. The movements of the series actuator 86therefore do not give rise to parasitic movements of the flight control.

It should be observed that the piloting assistance means may anchor theflight control mechanically and in static manner.

It suffices for the coefficient of friction between two moving membersof the piloting assistance means 100, e.g. between the gearing and theelectric motor 105, to be greater than the coefficient of friction ofthe elements of the linkage extending between the series actuator 86 andthe inlet of the servo-control 23.

In a non-essential variant, and with reference to FIG. 2, provision maybe made for a friction unit 85 to be provided that is dedicated to thispurpose between the series actuator 86 and the flight control 10, e.g.on the secondary second rod 84.

FIG. 4 is a diagram for explaining the method of the invention ingreater detail.

In a step a1), performed in real time, the instantaneous force beingsupported by the linkage 35 is measured using the instantaneous forcesensor 88.

During a step a11), in parallel with the step a1), the position of theflight control 10 is measured in real time using the positiondetermination means 89.

Finally, during a step b), an additional force is generated as afunction of the measured instantaneous force and the measured positionof the flight control 10.

Advantageously, during a step b1), the control means 104 determine asetpoint force for application to the linkage appropriate for theposition of the flight control 10 as measured during step a11).

For this purpose, the control means 104 rely on a pre-established forcerelationship. Specifically, the force relationship is given by a curvein a graph plotting position of the flight control along the abscissaand setpoint force up the ordinate.

Such a force relationship may correspond in particular to the forcerelationship induced by the torsion springs used in the state of theart.

In a variant of the invention, the control means 104 have a plurality offorce relationships available. Thus, the control means 104 are in aposition to determine automatically the force relationship that shouldbe used as a function of predetermined rules, possibly relating toflying conditions.

For example, the control means 104 determine the linkage 35 with whichthey are associated and they select the predetermined forcerelationship(s) to correspond with that linkage.

For this purpose, for each connector for connecting to a batch of plugsof the piloting assistance means 100, the control means 104 optionallydetermine the particular connector via which it is connected to theelectrical circuit of the rotorcraft, by determining which batch ofplugs is involved. Depending on the connector in use, the control meansthen determine the pertinent force relationship(s).

In addition, the control means 104 pass from a force relationship havinga shallow slope to a force relationship having a steep slope, and viceversa, as a function of the rate at which the flight control 10 ismoved. The control means 104 determine the speed of rotation of theelectric motor 105 by differentiating the angular position of theelectric motor as obtained via a first sensor for sensing the angularposition of the electric motor. Depending on the speed of rotationobtained in this way, the control means 104 change the forcerelationship.

Under such circumstances, the piloting assistance means 100 mayfavorably replace the dampers used in the known state of the art.

In the same way, the control means 104 may select a force relationshiphaving a very steep slope so that the piloting assistance means performthe function of a dynamic abutment. Consequently, the additional forceprovided by the piloting assistance means 100 is an opposing additionalforce that tends to prevent the pilot from moving the flight control.

In another variant, the pilot may instruct a changeover from one forcerelationship to another by using dedicated selector means.

During a step b2) in step b), the control means 104 determine anadditional force to be supplied, the additional force being equal to thedifference between the setpoint force and the instantaneous force.

Thereafter, during a step b3) of step b), and using a conversion table,the control means 104 determine the setpoint current for application tothe electric motor 105, and the direction of rotation of the electricmotor 105, so that the piloting assistance means 100 can generate therequired additional force. A method that implements broadband vectorcontrol is advantageously used.

Finally, during a step b4), the control means 104 feed the electricmotor with electricity at the setpoint current.

Furthermore, it is advantageous for the control means 104 to monitorelectricity consumption by the electric motor 105. If the control means104 detect excess consumption, then the control means 104 instruct fusemeans 103 to separate the piloting assistance means 100 from thelinkage, by separating the electric motor 105 from the outlet shaft 101.The control means 104 may signal a fault to a rotorcraft monitor member.

FIG. 5 is a diagram showing piloting assistance means 100 having twoelectric motors 105 for safety reasons.

In normal operation, the electric motors drive the gearing 102 together,each delivering an equal share. In contrast, in the event of one of theelectric motors 105 breaking down, the gearing 102 is driven by thestill-working electric motor 105.

Under drive from the electric motors 105, the gearing 102 is suitablefor rotating fuse means 103 secured to the outlet shaft 101.

The free end of the outlet shaft 101 then turns a crank 101′ hinged to alink rod 87.

In addition, the piloting assistance means 100 have one conventionalfirst position sensor 140 per electric motor. The first position sensors140 deliver information about the angular positions of their associatedelectric motors to the control means 104, e.g. an electronics card.

Furthermore, the piloting assistance means 100 are provided with atleast one second position sensor 150 for sensing the position of theoutlet shaft 101. The second position sensors 150 deliver informationabout the angular position of the outlet shaft 101.

The first and second position sensors thus form portions of the means 89for determining the position of the flight control 10.

By way of example, such a variant serves to avoid implementing an anglesensor on the flight control, unlike the version shown in FIG. 2.

Furthermore, with reference to FIGS. 5 to 7, the fuse means 103 isprovided with a first wheel 111 having a set of teeth 112 on its outerperiphery 111′. The teeth 112 of the first wheel then co-operate withthe gearing 102 via fluting.

Furthermore, the inner periphery 111″ of the first wheel 111 is securedto a crown of driving teeth 113. A ferric plate 114 is secured to thefirst wheel 111 by being arranged between the inner and outerperipheries 111″ and 111′ of the first wheel 111.

In addition, the fuse means 103 possess a crown of driven teeth 120secured to the outlet shaft 101. A support 131 is then secured to thedriven teeth so as to support an electric coil 130 controlled by thecontrol means 104.

A bearing 116, a friction washer 117, and a spring 115 are then arrangedaround the outlet shaft between the driving and driven teeth 113 and120.

Under such conditions, the spring tends to move the driving teeth 113away from the driven teeth 120 so as to separate the first wheel 111,and thus the electric motors 105, from the outlet shaft 101.

In the configuration shown, the first wheel 111 moves along the flutingof the gearing.

In an alternative configuration, the driving teeth are connected to theinner portion of the first wheel via fluting. The ferric plate is thensecured to the driving teeth and not to the first wheel, with it thenbeing possible for the driving teeth to move axially relative to thefirst wheel.

In contrast, when the control means 104 power the coil 130 electrically,the coil 130 generates a magnetic field that attracts the first wheel111 towards the coil 130 in spite of the opposing force from the spring115. The first wheel 111 moves along the outlet shaft while remainingconstrained to rotate with the gearing 102, until the driving teeth 113mesh with the driven teeth 120.

Finally, the control means 104 are advantageously provided with a maincomputer unit for controlling at least one electric motor and with amonitoring computer unit, these computer units comprisingmicroprocessors, for example.

The main computer unit performs multiple operations for deliveringorders to control the various members of the piloting assistance means.The monitoring computer unit then performs the same operations as themain computer unit and verifies that it obtains the same results. In theevent of disagreement, the monitoring computer unit deactivates thepiloting assistance means and informs the pilot.

Naturally, the present invention may be subjected to numerous variationsas to its implementation. Although several embodiments are described, itwill readily be understood that it is not conceivable to identifyexhaustively all possible embodiments. It is naturally possible toenvisage replacing any of the means described by equivalent meanswithout going beyond the ambit of the present invention.

What is claimed is:
 1. A piloting assistance device for assisting thepiloting of a rotorcraft, the rotorcraft being provided with a flightcontrol for controlling a rotor via at least one linkage provided with aplurality of rods including at least intermediate rod and link means,wherein the device comprises: an instantaneous force sensor secured toan intermediate rod; determination means for determining a position ofthe flight control; and piloting assistance means having at least oneelectric motor controlled by control means to drive an outlet shaftconnected to the link means in parallel with the at least one linkage,the piloting assistance means including at least a first position sensorfor determining an angular position of the at least one electric motor,and/or at least a second position sensor for sensing a position of theoutlet shaft.
 2. A piloting assistance device according to claim 1,further including at least one autopilot means for controlling thepiloting assistance means.
 3. A piloting assistance device according toclaim 1, further including a friction unit arranged between the controlmeans and a series actuator to generate a friction force greater thanthe friction force of a linkage between the series actuator and therotor.
 4. A piloting assistance device according to claim 1, wherein therotorcraft is provided with at least two linkages, each having aplurality of rods including at least one intermediate rod and linkmeans, the piloting assistance device further comprising oneinstantaneous force sensor arranged in the intermediate rod of anassociated linkage; and a single piloting assistance means per linkagethat is connected to the link means in parallel with the associatedlinkage.
 5. A piloting assistance device according to claim 1, whereinthe electric motor is connected to an outlet shaft successively viagearing and fuse means, the fuse means comprising a first wheel providedwith teeth on an outer periphery that co-operate with the gearing andwith driving teeth on an inner periphery, the driving teeth movingaxially relative to the gearing; driven teeth arranged on the outletshaft for co-operating with the driving teeth; and a stationaryelectrical coil for attracting the driving teeth against the driventeeth when the coil is electrically powered by the control means.
 6. Apiloting assistance device for assisting the piloting of a rotorcraft,the rotorcraft being provided with a flight control for controlling arotor via at least one linkage provided with a plurality of rodsincluding at least intermediate rod and link means, wherein the devicecomprises: an instantaneous force sensor arranged in an intermediaterod; determination means for determining a position of the flightcontrol; and piloting assistance means having at least one electricmotor controlled by control means to drive an outlet shaft connected tothe link means in parallel with the at least one linkage, the pilotingassistance means including at least a first position sensor fordetermining an angular position of the at least one electric motor, andat least a second position sensor for sensing a position of the outletshaft.
 7. A piloting assistance device for assisting the piloting of arotorcraft, the rotorcraft being provided with a flight control forcontrolling a rotor via at least one linkage provided with a pluralityof rods including at least intermediate rod and link means, wherein thedevice comprises: an instantaneous force sensor arranged in anintermediate rod; determination means for determining a position of theflight control; and piloting assistance means having at least oneelectric motor controlled by control means to drive an outlet shaftconnected to the link means in parallel with the at least one linkage,the piloting assistance means including a position sensor selected fromthe group consisting of a first position sensor for determining anangular position of the at least one electric motor and a secondposition sensor for sensing a position of the outlet shaft.